Technical Field
This disclosure relates to electronic systems and, in particular, to radio frequency (RF) couplers.
Description of the Related Technology
Radio frequency (RF) sources, such as RF amplifiers, can provide RF signals. When an RF signal generated by an RF source is provided to a load, such as to an antenna, a portion of the RF signal can be reflected back from the load. An RF coupler can be included in a signal path between the RF source and the load to provide an indication of forward RF power of the RF signal traveling from the RF amplifier to the load and/or an indication of reverse RF power reflected back from the load. RF couplers include, for example, direction couplers, bi-directional couplers, multi-band couplers (e.g., dual-band couplers), etc.
An RF coupler can have a coupled port, an isolated port, a power input port, and a power output port. When a termination impedance is presented to the isolated port, an indication of forward RF power traveling from the power input port to the power output port can be provided at the coupled port. When a termination impedance is presented to the coupled port, an indication of reverse RF power traveling from the power output port to the power input port can be provided at the isolated port. The termination impedance has been implemented by a 50 Ohm shunt resistor in a variety of conventional RF couplers.
An RF coupler has a coupling factor, which can represent how much power is provided to the coupled port of the RF coupler relative to the power of an RF signal at the power input port. RF couplers typically cause an insertion loss in an RF signal path. Thus, an RF signal received at the power input port of an RF coupler can have a lower power when provided at the power output port of the RF coupler. Insertion loss can be due to a portion of the RF signal being provided to the coupled port (or to the isolated port) and/or to losses associated with the main transmission line of the RF coupler.